Propulsive jet apparatus



Patented `une 19,` 1951 rRorULsIvE JET APPARATUS Roderick Cristall McLeod, Cropston, Leicester, England, assignor to Power Jets (Research & Development) Limited, London, England Application August 14, 1945, Serial No. 610,736 In Great Britain April 27, 1942` Section 1, Public Law 690, August 8, 1946 This invention relates to propulsive jet apparatus, and particularly to the jet or exhaust pipe of an aircraft or like propulsive system in which a power unit expels a stream of hot gas at high velocity. It has been found somewhat dincult in installations of such arrangements, to accommodate thermal expansions, whilst taking care of other factors. Where a jet pipe is lengthy and is supported by attachment to the power unit at its forward end, and by some form of suspension or support more rearwardly, it is difficult to arrange for exact alignment inthe complete installation, particularly in View of thermal expansions, and the loads which are applied to the system in use, such as loads due to accelerations. Moreover, the parts involved may be of comparatively light-gauge sheet metal and are not Well adapted to resist stresses tending to buckle them. Again, it may be desirable to preclude all reasonable possibility of gas leakage, and also to leave the internal surface of the pipe very smooth and flush. There may be considerable end load due to gas ow conditions, usually in the form of tension in the jet pipe.

Whilst it is desirable that the surface internal wall of the jet pipe should be smooth and uninterrupted in order to minimise loss of efficiency, it is found that a slight stepping (such as will be seen hereinafter) due to thickness of sheetmetal, can be regarded as insignicant and a wall having such a form can be regarded as substantially smooth for practical purposes. It is probably important however that such formatent expires April 27, 1962 (citizsw tions'should be minimised as far as possible, and

that uncontrolled open gaps or leakages, espocially in the region of such stepping, should be avoided since their presence may promote undue turbulence with consequent loss. If there were to be any substantial discontinuity of the pipe wallJ it would probably be preferable to make it deliberately in a properly designed and controlled manner, in which case it may not be undesirable. The present invention is however concerned with cases in which gas tightness is required.

According to this invention there is provided in a jet propulsion exhaust or jet pipe, a gastight flexible joint so arranged as to permit some flexibility of alignment without substantial resistance and such as to leave the internal wall of the pipe substantially smooth and uninterrupted. It will be appreciated that a pipe of comparatively large diameter even if made of thin sheet metal, is very rigid in bending and can offer such substantial resistance that high stresses can be imposed by tendencies-to bend 2 for example due to deflections in an aircraft structure; the object of the joint is to afford relatively low resistance to deflections, particularly of alignment, whilst preserving gas tight- V neSS.

The invention further provides in a jet propulsion power plant for aircraft, an exhaust or jet pipe having a virtually continuous and smooth internal wall with a flexible and gas tight joint between adjacent lengths or sections of the pipe to permit flexing of the pipe as a whole (e. g., deflections from strict alignment) lwithout substantial resistance, the joint comprising a radially extending structure having the requisite flexibility and in hermetic sealed attachment to the pipe sections, the ends of these sections being arranged to mate with freedom for relative movement without substantial breaking of the smooth continuity of the pipe wall. In view of the fact that end-wise or axial loads may have to be transmitted from one length or section of the jet pipe to the other, means may be provided for transmitting such loads and more especially tension, across the joint without impeding flexibility at least about one plane; it may here be mentioned that it is anticipated that serious deflections of the structure or pipe are only to be expected in one plane and in such cases it may therefore be sufficient to aiiord ilexible freedom about one plane which in present conceptions is a horizontal plane. The structure of the ilexible parts is preferably in the form of outwardly extending webs or anges of sheet metal attached in a hermetic gas-tight manner in the region of the joint to the adjacent pipe sections, these webs being inter-attached towards their outer margins also in gas-tight manner; they may in eiect be nat annular plates inter-attached through an annular rim which spaces them. The material forming the wall of the pipe is intended to be sheet metal or other thin metal, and the pipe sections where they mate are preferably provided with a spigot type of joint in such a manner as to present a substan-A tially smooth continuous inner surface whilst permitting the required slight relative movement between the sections, the joint as a whole not depending upon the spigot to be gas-tight.

'Pipe joints are already known in which there is vprovision for slight universal angular movement, or for expansion and contraction whilst leaving the internal wall of the pipe substantially smooth and uninterrupted; in some of these, iiexible corrugated or bellows-like but fluid-tight structures surround a spigot joint and it has been,

3 proposed to provide tension linking between the two pipes which are joined to prevent undue stressing of the flexible structure. No claim is made herein to the construction of such joints as such. *The presentfinvention is=`concerned with the application of joints having certain attributes to the particular case of jet propulsion wherein special problems arise.

The invention is illustrated in the :accompanying drawing in which Fig. l is a diagrammatic external view in plan, Fig.`'2 an-erilargedlpartial sectional view and Fig. 3 a s'crapwiew'in fthe direction of the pipe axis.

In these gures, I represents an upstreampipe length which is intended to be a sectionformig virtually a permanent part of the ,power unit constituted in this case by "an 4exhaust d'u'ct immediately behind a gas turbine and containing an internal co-axial conical fairing indicate'dr'at 2. The downstream length of the jet pipe is -shown at 2, this being plaincylindrical-ppe. :It

is'between these two sections that a .degree-'o flexibility is required about a'horizontaldiameter. Thepipe section I is constructed mainly ofsheet mtal andto it is attached, for example by welding, a short extension sleeve3 to which is in turn attached by welding, rivetting or the like, .an annular radially extending plate or web 4. `Simi- Vlarly attached to the pipe lengthl2 is a second web A5. At `the outer .margins these webs .are inter-attached through an annular rim` Shaving nbre or like heat resistant gaskets 'I on each-side,

this inter-attachment preferably vbeingby-.bolts and nuts represented at8 for detachability of the sections. The sleeve 3 overlapsrthefend .of

the pipe'lengtlrrZ` and between these/there lisa libre packing 9. 'Ifhe end of the-lengthL-may have axially directed slits I in its skirt to. afford ilex'ibility and freedomfor relative movement-by aording flexibility. In "Fig, 2 it will bemseen that the adjacent ends of pipe lengthsl and 2. present a gap indicated at I I and this haslbeen somewhat exaggerated in the drawing.v In actual practise this `gap willbe'left only suiciently large to permit the required degree-ofrnisalignend of the section 2 and the sleeveS is .notllin itself an effectively gas tight joint,`but .that gas tightness is aioi'ded by the fact that thestructure 4, 5, 6, 'I is gas tight.

Endwise loads are transmitted between .`the pipe lengths across thek joint so.constituted'loy` a pair of stirrup-like links I2 which v'circumvent the web structure. -The link-'I2 is attachedby the pins I3 which are preferablycontrived soas to be easily removable to bosses I4 whichrare in Yturn attached to `flanges I5 provided externally` on the pipey sections. `Theseflanges.incidentally reinforce the ends of the pipe lengths to. maintain their circularity.

The construction above described'is'as vstated 4based on the assumption -that .expectant ldeflections will be mainly in` one plane. y"'Iheremay however be cases lwhere deflections or A.mal-

--alignment'tend to rise in various di-rectionsfand in 'such/case it is proposed'to 4provide-.a plurality about the axis of the pipe and to attach the links to the pipe lengths with some freedom of movement so that axial loads between the pipe lengths will always be met by at least one link. In the construction described it will be `seen that detachment I'is a 'fairly simple matter, `merely involving the removal of the links I2 and the bolts 58 with subsequent dis-engagement of the mating that :since @gas-tightness depends ultimately on spigot and socket joint` It may also be remarked fthat vfsince gas-tightness depends ultimately on th'e joint .made at the margin oi' the flexible structure-andfthis margin is deliberately some- 'what.flexible,it is not diflcult to achieve a good ,joint without having to take excessive care in manufacturing and fitting.

"'I "claim: 1. Ajetpropulsion jet pipe having axially successive coaxial pipe sections mutually arranged end to end to be capable of longitudinal movementland lateral angular deilection one relative .to .theothen and. interconnecting means between .said sections, saidinterconnecting means comprising ygas-tight pliable jointing means adapted .toyieldlexibly without substantial resistance to yaccommodate either deflecting or longitudinal loads, and means for relieving said jointing means of axially directed loads, said interconnecting ,meansbeing wholly external to said pipe sections Aand .thelatterpresenting a'substantially smooth 11n-interrupted internal surface.

2. :A jet-propulsion jet pipe comprising two lengths of pipe of vequal internal en'd diameter varrangedendto.end so as tovbe capable of' lateral angular deflection one relative to the other, a pliable sealing .structure attached 'hermetically lto`bo'th lengths of pipe externally thereof, said A.sealing structure'being adapted to yield iiexibly .to.. accommodate either. deflecting or'longitudinal .1oads,-an'd means to transmit axially directed loadsfrom .one pipelength to thev other to the .exclusion Vof .said sealing structure while per- .mitting said deflection and longitudinal movement andexible distortion of said sealing structure.

"3. A jet-propulsion jet pipe comprising two .lengths of pipe of equal internal end diameter .arranged endlto end so as to be capable of-lateral angular deflectionone relative 'to "the other, `a .pliable sealing vstructure attached hermetically 'toboth' lengths of pipe externally thereof, said sealing `structure including a tubular element overlapping and surrounding'the adjacent ends of the lengths of pipe, hermetically :attachedto one of the pipelengths and slidably engaging the otherpipe length within said sealing structure, said pliable sealing structure being adapted .toyield-ilexiblyl to. accommodate either delecting or longitudinal 4loads, and means to transmit axiallydire`cte'd loads from one ypipe' length' to ltheother tothe exclusion of said sealing struc- 4 ture whilepermi'tting said deilection and lonv gitudinal movement and exible distortion of said sealing structure.

4.!A'jet-propulsionjet pipe comprising two #lengths of pipeqof .equal ,internal end 'diameter arranged end to end so as to. be capable of lateral .angular deflection one relative to Lthe other, a sealing4 structure.. attached hermeticallyY to .both

.- qlengths of -pipe externally thereof,- said sealing structure being adapted toyield ilexibly toaccom- .,modate either `derlecting or longitudinalloads,

l and twolink members attached externallyto4 both fleng'thsof `rpipeat diametricallyopposite loca- 1 of'links such as'l2 arranged forfexampleat 20 fa'ML-tionssaid link members `yielding elastically. `tc

accommodate longitudinal relative movement of said pipe lengths and also to permit said angular deilection approximately about that diameter while transmitting axially directed loads from one pipe length to the other.

5. A jet-propulsion jet pipe comprising two lengths of pipe of equal internal end diameter arranged end to end so as to be capable of lateral angular deflection one relative to the other, a sealing structure attached hermetically to both lengths of pipe externally thereof, and said sealing structure being adapted to yield flexibly to accommodate either deflecting or longitudinal loads, link members attached externally to both lengths of pipe to transmit axially directed loads from one pipe length to the other, said link members yielding elastically to accommodate longitudinal relative movement of said pipe lengths and also to permit said angular deection of one pipe length relative to the other and consequent deformations of said structure, said link members lying wholly outside and extending radially beyond said structure.

6. A jet-propulsion jet pipe comprising two lengths of pipe arranged substantially aligned and being mutually engaged by a spigot arrangement alfording sliding freedom, said pipe lengths being capable of lateral angular deflection relative one to another, a sealing structure attached hermetically to both lengths of pipe externally thereof, said sealing structure being adapted to yield flexibly to accommodate either deiiecting or longitudinal loads, and link members attached externally to both lengths of pipe to be capable of transmitting axial loads from one length to the other, said link members yielding elastically by distortion of their structure to permit said angular relative deflection between said lengths.

7. A jet pipe according to claim 6, in which the said flexible sealing structure comprises radially extending annular walls joined to the respective pipe lengths at their inner margins and jointed together in the region of their outer margins.

8. A jet-propulsion jet pipe having axially successive coaxial pipe sections mutually arranged to be capable of longitudinal movement and lateral angular deflection one relative to the other, and interconnecting means between said sections, said interconnecting means comprising gas-tight pliable jointing means adapted to yield without substantial resistance to accommodate either deflecting or longitudinal loads and axialload transmitting connecting means adapted to yield to accommodate said deflection and movement while sustaining to the exclusion of said jointing means axial-load between said sections, both said jointing and axial-load transmitting means being arranged externally of said pipe sections so that the latter, apart from any end clearance between them, present internally a substantially smooth uninterrupted surface.

RODERICK CRISTALL MCLEOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 332,906 Karwiese Dec. 22, 1885 1,037,554 Shoemaker Sept. 3, 1912 1,871,627 Massa Aug. 16, 1932 1,974,780 Mann Sept. 25, 1934 2,318,006 Mercier May 4, 1943 2,337,038 Fentress Dec. 21, 1943 

